[113.05] Serendipitous Discovery of the 2175 Angstrom Dust Feature at High Redshift from the Sloan Digital Sky Survey

J. Wang, J. Ge (Penn. State), P.B. Hall (Princeton Univ.)

We report direct detection of the 2175Å absorption
feature due to extinction by dust grains, which is seen in
the Milky Way and Large Magellanic Cloud extinction curves
but has been searched for over decades in intervening
absorption systems at high redshift. Two quasars at
redshifts 2< z <3 from the SDSS Data Release 1 exhibit the
2175Å bump from intervening absorption systems at
zabs ~ 1.4, the first time this feature has been
detected in individual intervening Mg\,II systems. The
rest-frame FWHM of the absorption feature matches the
expected FWHM of ~q 350Å. We investigate the
possible dust grain type by applying reddening with the
empirical extinction curves for the Milky Way, LMC and SMC,
and with a range of E(B-V), to various composite quasar
spectra from the SDSS to determine the best-fit intrinsic
spectrum, extinction curve, and reddening. We further
calculate the dust-to-gas ratios at the absorber redshifts
to explore dust formation at high redshift.

This work was supported by NASA grants NGA5-12115,
NAG5-11427, NSF AST-0138235 and the Penn State Eberly
College of Science.

The author(s) of this abstract have provided an email address
for comments about the abstract:
jwang@astro.psu.edu